1. Field of the Invention
The present invention relates to a device for detecting or diagnosing an abnormal/failure state of an electronic circuit, and particularly relates to a circuit board inspection device for predicting, detecting or preventing abnormality/failure in operation or performance of an electronic circuit, for example, in equipment having the electronic circuit which is called PWBA formed out of a plurality of circuit boards connected with one another.
Also, the present invention relates to a method for performing prediction or detection of abnormality or failure in operation or performance (hereinafter collectively referred to as “failure diagnosis”) of circuit members in apparatus having a circuit board mounted with the circuit members, such as a printer, a facsimile machine or a multi-function machine having the same functions as the printer and the facsimile machine; a failure diagnosis system for effectuating the failure diagnosis method; and a printed wiring board for use in the failure diagnosis system.
2. Description of the Related Art
In recent years, with improvement in performance and function of electronic equipment such as personal computers or copying machines, more and more analog and digital electronic circuits for various applications for achieving the improvement have been stored in the form of printed boards. In addition, a large number of electronic circuit boards having high reliability and capable of operating at a high speed and with a high accuracy are mounted as means for operation control or the like in other industrial equipment such as automobiles, aircraft, robots, or semiconductor designing devices. When these electronic circuit boards are connected through cables in various forms, desired specifications for implementing a series of functions can be achieved.
Equipment mounted with such boards is used typically in an office or in a house, but may be used in an oppressive environment in some cases. Thus, the environment where such equipment is used is in a wide range. Particularly in a bad environment where the equipment is used, various abnormalities or failures difficult to be detected may occur in spite of normal use. Thus, a great deal of labor is required for restoring the equipment.
Even when the equipment is used in a normal environment, there may occur an abnormality or a failure in the electronic circuits. The location where the abnormality or the failure has been detected cannot be identified frequently though it cannot be the that the frequency of such an abnormality or a failure is low. Further, once there occurs an abnormality in the electronic circuit boards, a prompt countermeasure must be taken in view of safety, cost and so on.
As an example of such a countermeasure, when a person who is in charge of repairs is notified of information of abnormality or failure in a copying machine or a printer, the person in charge of repairs may rush to the scene to specify a failure location on the basis of failure location information, failure history information or the like recorded in the equipment and take action such as exchange or repair.
Alternatively, when such equipment is connected to a network so as to transmit information such as condition management or failure information automatically to a station for managing such information, the person in charge of repairs may analyze the information before taking such action.
However, when there occurs abnormality or failure as described previously, the equipment is usually out of commission, causing a downtime disadvantageously to the user side.
On the other hand, the maker side also faces the following situation. That is, it may take much labor to specify the failure location, or it is not always possible to specify the failure location correctly. Thus, it may cost a great deal to exchange all the possible parts for the failure. Alternatively, it may take much time for repair per se, or action to be taken may be delayed due to limited manpower. Thus, in fact, both the user side and the maker side are often in a situation leading to a great loss.
Therefore, to specify a failure location or to predict the occurrence of a failure per se, various approaches such as an approach to increase accuracy to specify the failure location, an approach to reduce a temporal loss in specifying the failure location, an approach to grasp various abnormal conditions or failure conditions without exception, and an approach to realize these approaches with a simple configuration and at a low cost have been taken.
One example is disclosed in “Detection of Flaws in a Printed Circuit Board by Using an Eddy-Current Testing Approach” (2002, written by Hisashi Fujiki et al. Faculty of Engineering, Kanazawa University
http://magmac1.ec.t.kanazawa-u.ac.jp/magcap-j/research-j/ec ta-j.html, searched on Dec. 4, 2002).
This technique detects abnormalities by a non-contact method using a magnetic field detection probe small in size and unique in shape. The magnetic field detection probe detects a magnetic field generated from a current flowing through a target wire. When the magnetic field detection probe scans wiring of a board in a non-contact manner, abnormalities occurring in an existing high-density wiring printed board, including failures of ICs as well as disconnection/line-width abnormalities of the wiring in the board are detected in a high-speed and mechanical-stress-free state.
On the other hand, JP-A-2000-74998 specifies a failure in the following manner. That is, a power supply current for each electronic board is allowed to flow into a resistor connected in parallel with a power supply. Current information of the electronic board is read based on a potential difference between the opposite ends of the resistor, and compared with that in a normal state, so that a failure is judged.
However, such a circuit board inspection device has the following problems. That is, according to the technique disclosed in “Detection of Flaws in a Printed Circuit Board by Using an Eddy-Current Testing Approach”, the conditions of a signal line on the circuit board or the magnetic field generated from the current flowing through the signal line can be sensed in a non-contact manner and with high accuracy, but an exclusive probe used as means for sensing the magnetic field is so expensive that it costs much to detect a failure. In addition, the area which can be measured at one time is a pinpoint. Thus, there occurs a problem that it takes much time or much labor to inspect a failure over the whole area of the circuit board.
On the other hand, according to the technique disclosed in JP-A-2000-74998, for example, a sensing portion has to be incorporated at the time of designing the circuit board and used fixedly. Thus, there occurs a problem that the technique is poor in flexibility of arrangement.
According to a typical method of failure diagnosis, a failure location is specified with voltages or signal waveforms in major locations monitored by means of a measuring device such as a tester. Since various locations have to be measured in such a diagnosis method, there is however a problem that it takes much labor for failure diagnosis to thereby result in deterioration of working efficiency.
Therefore, as a more efficient diagnosis method, there is a self-diagnostic system (Diagnostics system). According to the Diagnostics system, upon starting etc. of apparatus, the apparatus per se diagnoses a failure in each board or each electronic circuit. In the Diagnostics system, a failure diagnosis circuit for monitoring the circuit operation is provided at the time of designing electronic circuits. For example, a signal pattern (expected value) during the operation of the apparatus is monitored in every circuit module or every board or every circuit portion, and stored in advance. An output of the diagnosis circuit during actual operation is compared with the expected value. Thus, the existence of failure occurrence is diagnosed, and a failure location is specified.
On the other hand, with the recent improvement of performance and function, the operation of electronic circuits becomes more and more complicated. For this reason, the number of locations and the data width of each signal to be monitored for detecting a failure increase so that the scale of the failure diagnosis circuit increases. As a result, there is a problem that the number of man-hours for design increases so that the cost of the electronic circuits increases.
Therefore, to specify a failure location or to predict the occurrence of a failure per se, various approaches such as an approach to increase accuracy to specify the failure location, an approach to reduce a temporal loss in specifying the failure location, an approach to grasp various abnormal conditions or failure conditions without exception, and an approach to realize these approaches with a simple configuration and at a low cost have been taken.
For example, JP-A-11-38111 discloses apparatus for detecting a magnetic field generated by a current flowing through an electronic circuit. The apparatus proposed in JP-A-11-38111 measures a magnetic field generated from a current flowing through only one wire in circuit wiring of a printed circuit board or an LSI mounted in high density, at high resolution and in a non-contact manner while suppressing the influence of adjacent wires of the circuit wiring. With such apparatus, the operation of an electronic circuit to be failure-diagnosed can be monitored without providing a diagnosis circuit in the electronic circuit.
However, according to the method disclosed in Patent Document 1, the conditions of a signal line on the circuit board or the magnetic field generated from the current flowing through the signal line can be sensed in a non-contact manner and with high accuracy, but an expensive exclusive probe (sensing probe) has to be used as means for sensing the magnetic field. Thus, it costs much to detect a failure.
In addition, in order to check the conditions of any desired wire or terminal, the sensing probe has to be brought close to the vicinity of the wire or terminal for observation. This is because the detectable range of one probe is so narrow that the probe has to be brought close to a location to be diagnosed in order to diagnose the location accurately. Accordingly, for example, as shown in FIG. 21, as the means for bringing the probe close to a target portion, it is necessary to adopt a manner using manual operation, or to move the probe by use of mechanical means. It is therefore difficult to perform measurement in the state where the electronic circuit board is installed in a system such as electronic equipment, and it is necessary to perform failure diagnosis over the electronic circuit board off-line. As a result, it has to take much time and much labor. In addition, it is difficult to fix the position relation between the probe and the portion to be inspected. Thus, it is difficult to perform accurate inspection.
The circuit operation may be monitored all over the electronic circuit board with a plurality of exclusive probes installed in the system in order to monitor the circuit operation in a plurality of desired ranges. However, it costs a great deal for such a case. On the other hand, without adopting such a moving manner or with a small number of probes installed, only a range or ranges near the probe(s) can be detected. Thus, the detectable range becomes very narrow.
Thus, the related-art failure diagnosis method is not always user-friendly in view of the cost and the degree of freedom in setting a portion to be failure-diagnosed.